From Micropores to Ultra-micropores inside Hard Carbon: Toward Enhanced Capacity in Room-/ Low-Temperature Sodium-Ion Storage

Pore structure of hard carbon has a fundamental influence on the electrochemical properties in sodium-ion batteries(SIBs).Ultra-micropores(<0.5 nm)of hard carbon can function as ionic sieves to reduce the diffusion of slovated Na+but allow the entrance of naked Na^(+) into the pores,which can reduce the interficial contact between the electrolyte and the inner pores without sacrificing the fast diffusion kinetics.Herein,a molten diffusion-carbonization method is proposed to transform the micropores(>1 nm)inside carbon into ultra-micropores(<0.5 nm).Consequently,the designed carbon anode displays an enhanced capacity of 346 mAh g^(−1) at 30 mA g^(−1) with a high ICE value of~80.6%and most of the capacity(~90%)is below 1 V.Moreover,the high-loading electrode(~19 mg cm^(−2))exhibits a good temperature endurance with a high areal capacity of 6.14 mAh cm^(−2) at 25℃ and 5.32 mAh cm^(−2) at −20℃.Based on the in situ X-ray diffraction and ex situ solid-state nuclear magnetic resonance results,the designed ultra-micropores provide the extra Na+storage sites,which mainly contributes to the enhanced capacity.This proposed strategy shows a good potential for the development of high-performance SIBs.

降低全聚合物太阳能电池光伏效率的温度依赖性

全聚合物太阳能电池(All-PSCs)具有良好的机械稳定性和热稳定性,受到人们的广泛关注.目前,提高全聚合物太阳能电池性能的关键是改善活性层的形貌.本文通过逐层(LBL)工艺,优化了薄膜形貌,实现了更好的电荷产生和传输,增加了激子扩散长度,提高了电荷产量,并抑制了复合损失.此外,本文进一步研究了LBL制备的全聚合物太阳能电池中的激子/电荷行为与温度的依赖性关系.详细的原位光谱测量和光电特性表征表明,独特的形态延长了激子寿命,减少了电荷陷阱,并促进了电荷传输和收集.因此,准双层PM6/PYF-T-o器件的能量转换效率(PCE)显著提高(16.70%).此外,与BHJ器件相比,通过LBL工艺制备的器件,实现了增强的分子有序性,降低了能级混乱度,使得器件填充系数和PCE温度依赖性减弱.本工作为太阳能电池在温度可变环境下的电荷传输行为和光伏性能提供了新的认识,也为其实际应用提供了理论依据.

Improved demodulation method for fibre optic sensors applied in transformer partial discharge detection

The 2×2 couplers,as a demodulation core of the fibre optic sensing system,have been extensively employed in fibre optic sensors for partial discharge(PD)detection of power equipment.However,the unstable demodulation sensitivity and low signal-to-noise ratio(SNR)of such a system are still unsatisfactory in engineering.This work uses a distributed feedback fibre laser as the sensor and employs a common asymmetric 2×3 coupler instead of a 2×2 coupler as the demodulation core to design a PD detection system.Then,we propose a new demodulation method for PD acoustic emission signals based on the Naval Postgraduate School method.On the PD detection platform,the performance of the conventional detection system and the proposed system is compared.The experimental results show that the proposed system has better reliability and can identify the PD signals in all instances.Furthermore,the average SNR of the new demodulation method is 6.11 dB higher than the traditional 2×2 coupler system and can be extended to most PD detection systems using fibre optic sensors.

Automatic Generation Control with Virtual Synchronous Renewables

As synchronous generators(SGs)are gradually displaced by renewable energy sources(RESs),the frequency stability of power systems deteriorates because RESs,represented by utility-scale solar and wind power sources,do not provide the inertial response,primary frequency response,secondary frequency response,and tertiary frequency regulation.As a result,the remaining SGs may not be sufficient to maintain the power balance and frequency stability.The concept and control strategies of virtual synchronous generators(VSGs)enable the inverter-based wind and solar power sources to emulate the outer characteristics of traditional SGs and participate in the active power and frequency control of power systems.This paper focuses on the automatic generation control(AGC)with virtual synchronous renewables(VSRs).First,the VSR strategy that enables the RESs to participate in AGC is introduced.Second,based on the interval representation of uncertainty,the output of RES is transformed into two portions,i.e.,the dispatchable portion and the stochastic portion.In the dispatchable portion,the RESs can participate in AGC jointly with SGs.Accordingly,a security-constrained economic dispatch(SCED)model is built considering the RESs operating in VSR mode.Third,the solution strategy that employs the slack variables to acquire deterministic constraints is introduced.Finally,the proposed SCED model is solved based on the 6-bus and 39-bus systems.The results show that,compared with the maximum power point tracking(MPPT)mode,VSRs can participate in the active power and frequency control jointly with SGs,increase the maximum penetration level of RESs,and decrease the operating cost.

Chlorinated phthalimide polymer donor as ultra-wide bandgap and deep HOMO guest for achieving highly efficient polymer solar cells

Quaternary approach has been receiving more and more attention due to its effectiveness in improving solar cell performance, while synthesis/selection of the fourth component is yet a key issue. Herein, we report a chlorinated phthalimide based donor polymer(namely Ph I-Cl) having an ultra-wide bandgap(2.10 e V) and a deep HOMO(-5.58 e V) level. Addition of Ph I-Cl as the third component of PM6:Y6 and the fourth of PM6:Y6:PC71BM increases both hole and electron mobilities and gives rise to more balanced charge carriers mobilities. Both the short-circuit current-density and fill-factor are increased and open-circuit voltage is well maintained, delivering 17.0% and 18.1% efficiencies, respectively. These results demonstrate that chlorination on the side thiophene of phthalimide-based donor polymer is a way to make deep HOMO and ultra-wide bandgap donor polymer guest used for highly efficient ternary and quaternary strategies.

Humidity sensor and ultraviolet photodetector based on carrier trapping effect and negative photoconductivity in graphene quantum dots

We report on the experimental realization of a graphene quantum dots （GQD）-based htunidity sensor and ultraviolet （UV） photodetector. We demonstrate that the conductance of the GQD increases linearly with increasing relative humidity （RH） of the surrounding environment due to the carrier trapping effect, which forms the basis of a humidity sensor. When the sensor is operated in the dark state, the sensitivity can reach as high as 0.48 nS RH-^1. The GQD are also found to exhibit light intensity dependent negative photoconductivity under the UV irradiation, which can be exploited for UV detection. As a result of these carrier trapping and de-trapping processes, the performance of the photodetector can be significantly improved with the increasing RH, and the photoresponsivity can reach a high value of-418.1 μA W^-1 in the high humid state of RH=90%.